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 $242.34   4.718%   $253.7736   $253.77   $253.75   $253.80  
  Purchase #2 $201.56   13.501%   $228.7726   $228.77   $228.75   $228.80  
  Purchase #3 $194.52   12.831%   $219.4789   $219.48   $219.50   $219.50  
  Purchase #4 $172.68   6.142%   $183.286   $183.29   $183.30   $183.30  
  Purchase #5 $31.67   13.302%   $35.8827   $35.88   $35.90   $35.90  
  Purchase #6 $17.47   11.261%   $19.4373   $19.44   $19.45   $19.40  
  Purchase #7 $98.92   5.212%   $104.0757   $104.08   $104.10   $104.10  
  7 purchase totals = $959.16       $1,044.7068   $1,044.71   $1,044.75   $1,044.80