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 $211.44   9.744%   $232.0427   $232.04   $232.05   $232.00  
  Purchase #2 $120.52   7.403%   $129.4421   $129.44   $129.45   $129.40  
  Purchase #3 $218.32   10.266%   $240.7327   $240.73   $240.75   $240.70  
  Purchase #4 $203.66   4.757%   $213.3481   $213.35   $213.35   $213.30  
  Purchase #5 $44.32   13.776%   $50.4255   $50.43   $50.45   $50.40  
  Purchase #6 $207.58   5.655%   $219.3186   $219.32   $219.30   $219.30  
  Purchase #7 $101.26   8.474%   $109.8408   $109.84   $109.85   $109.80  
  7 purchase totals = $1,107.10       $1,195.1505   $1,195.15   $1,195.20   $1,194.90