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 $152.94   11.286%   $170.2008   $170.20   $170.20   $170.20  
  Purchase #2 $141.81   13.460%   $160.8976   $160.90   $160.90   $160.90  
  Purchase #3 $84.37   8.470%   $91.5161   $91.52   $91.50   $91.50  
  Purchase #4 $250.93   4.765%   $262.8868   $262.89   $262.90   $262.90  
  Purchase #5 $199.90   9.350%   $218.5907   $218.59   $218.60   $218.60  
  Purchase #6 $189.74   11.323%   $211.2243   $211.22   $211.20   $211.20  
  Purchase #7 $94.34   10.457%   $104.2051   $104.21   $104.20   $104.20  
  7 purchase totals = $1,114.03       $1,219.5214   $1,219.53   $1,219.50   $1,219.50