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 $201.58   9.813%   $221.361   $221.36   $221.35   $221.40  
  Purchase #2 $76.85   11.350%   $85.5725   $85.57   $85.55   $85.60  
  Purchase #3 $167.41   6.393%   $178.1125   $178.11   $178.10   $178.10  
  Purchase #4 $126.58   7.375%   $135.9153   $135.92   $135.90   $135.90  
  Purchase #5 $250.40   13.785%   $284.9176   $284.92   $284.90   $284.90  
  Purchase #6 $152.43   10.434%   $168.3345   $168.33   $168.35   $168.30  
  Purchase #7 $58.52   3.674%   $60.67   $60.67   $60.65   $60.70  
  7 purchase totals = $1,033.77       $1,134.8834   $1,134.88   $1,134.80   $1,134.90