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 $191.42   6.120%   $203.1349   $203.13   $203.15   $203.10  
  Purchase #2 $179.38   11.308%   $199.6643   $199.66   $199.65   $199.70  
  Purchase #3 $39.60   4.181%   $41.2557   $41.26   $41.25   $41.30  
  Purchase #4 $28.47   12.595%   $32.0558   $32.06   $32.05   $32.10  
  Purchase #5 $190.52   12.390%   $214.1254   $214.13   $214.15   $214.10  
  Purchase #6 $97.58   13.625%   $110.8753   $110.88   $110.90   $110.90  
  Purchase #7 $201.58   10.714%   $223.1773   $223.18   $223.20   $223.20  
  7 purchase totals = $928.55       $1,024.2887   $1,024.30   $1,024.35   $1,024.40