Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $128.59   13.200%   $145.5639   $145.56   $145.55   $145.60  
  Purchase #2 $222.36   3.820%   $230.8542   $230.85   $230.85   $230.90  
  Purchase #3 $107.28   13.815%   $122.1007   $122.10   $122.10   $122.10  
  Purchase #4 $166.98   4.855%   $175.0869   $175.09   $175.10   $175.10  
  Purchase #5 $163.47   7.838%   $176.2828   $176.28   $176.30   $176.30  
  Purchase #6 $240.86   11.307%   $268.094   $268.09   $268.10   $268.10  
  Purchase #7 $217.72   9.869%   $239.2068   $239.21   $239.20   $239.20  
  7 purchase totals = $1,247.26       $1,357.1893   $1,357.18   $1,357.20   $1,357.30