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 $179.43   8.146%   $194.0464   $194.05   $194.05   $194.00  
  Purchase #2 $217.78   11.161%   $242.0864   $242.09   $242.10   $242.10  
  Purchase #3 $39.53   7.129%   $42.3481   $42.35   $42.35   $42.30  
  Purchase #4 $193.40   5.353%   $203.7527   $203.75   $203.75   $203.80  
  Purchase #5 $15.85   7.711%   $17.0722   $17.07   $17.05   $17.10  
  Purchase #6 $173.35   4.717%   $181.5269   $181.53   $181.55   $181.50  
  Purchase #7 $147.41   3.849%   $153.0838   $153.08   $153.10   $153.10  
  7 purchase totals = $966.75       $1,033.9165   $1,033.92   $1,033.95   $1,033.90