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 $83.52   12.788%   $94.2005   $94.20   $94.20   $94.20  
  Purchase #2 $93.60   11.716%   $104.5662   $104.57   $104.55   $104.60  
  Purchase #3 $114.29   13.435%   $129.6449   $129.64   $129.65   $129.60  
  Purchase #4 $194.63   3.717%   $201.8644   $201.86   $201.85   $201.90  
  Purchase #5 $159.83   11.645%   $178.4422   $178.44   $178.45   $178.40  
  Purchase #6 $211.97   12.463%   $238.3878   $238.39   $238.40   $238.40  
  Purchase #7 $51.82   10.502%   $57.2621   $57.26   $57.25   $57.30  
  7 purchase totals = $909.66       $1,004.3681   $1,004.36   $1,004.35   $1,004.40