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 $207.59   12.624%   $233.7962   $233.80   $233.80   $233.80  
  Purchase #2 $53.93   13.858%   $61.4036   $61.40   $61.40   $61.40  
  Purchase #3 $97.53   7.506%   $104.8506   $104.85   $104.85   $104.90  
  Purchase #4 $225.73   4.282%   $235.3958   $235.40   $235.40   $235.40  
  Purchase #5 $12.68   7.683%   $13.6542   $13.65   $13.65   $13.70  
  Purchase #6 $204.38   9.146%   $223.0726   $223.07   $223.05   $223.10  
  Purchase #7 $143.98   11.143%   $160.0237   $160.02   $160.00   $160.00  
  7 purchase totals = $945.82       $1,032.1967   $1,032.19   $1,032.15   $1,032.30