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 $54.96   10.112%   $60.5176   $60.52   $60.50   $60.50  
  Purchase #2 $195.35   8.396%   $211.7516   $211.75   $211.75   $211.80  
  Purchase #3 $55.40   12.430%   $62.2862   $62.29   $62.30   $62.30  
  Purchase #4 $140.54   7.362%   $150.8866   $150.89   $150.90   $150.90  
  Purchase #5 $136.67   9.362%   $149.465   $149.47   $149.45   $149.50  
  Purchase #6 $218.33   12.868%   $246.4247   $246.42   $246.40   $246.40  
  Purchase #7 $118.56   6.541%   $126.315   $126.32   $126.30   $126.30  
  7 purchase totals = $919.81       $1,007.6467   $1,007.66   $1,007.60   $1,007.70