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 $80.76   9.112%   $88.1189   $88.12   $88.10   $88.10  
  Purchase #2 $56.39   4.594%   $58.9806   $58.98   $59.00   $59.00  
  Purchase #3 $121.36   9.559%   $132.9608   $132.96   $132.95   $133.00  
  Purchase #4 $201.45   13.122%   $227.8843   $227.88   $227.90   $227.90  
  Purchase #5 $10.73   12.362%   $12.0564   $12.06   $12.05   $12.10  
  Purchase #6 $180.30   7.822%   $194.4031   $194.40   $194.40   $194.40  
  Purchase #7 $247.99   13.467%   $281.3868   $281.39   $281.40   $281.40  
  7 purchase totals = $898.98       $995.7909   $995.79   $995.80   $995.90