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 $179.28   13.177%   $202.9037   $202.90   $202.90   $202.90  
  Purchase #2 $169.48   7.187%   $181.6605   $181.66   $181.65   $181.70  
  Purchase #3 $174.88   4.594%   $182.914   $182.91   $182.90   $182.90  
  Purchase #4 $111.94   11.155%   $124.4269   $124.43   $124.45   $124.40  
  Purchase #5 $156.46   4.295%   $163.18   $163.18   $163.20   $163.20  
  Purchase #6 $31.74   3.212%   $32.7595   $32.76   $32.75   $32.80  
  Purchase #7 $37.47   4.415%   $39.1243   $39.12   $39.10   $39.10  
  7 purchase totals = $861.25       $926.9689   $926.96   $926.95   $927.00