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 $93.42   9.266%   $102.0763   $102.08   $102.10   $102.10  
  Purchase #2 $92.78   12.553%   $104.4267   $104.43   $104.45   $104.40  
  Purchase #3 $84.97   3.634%   $88.0578   $88.06   $88.05   $88.10  
  Purchase #4 $180.83   12.452%   $203.347   $203.35   $203.35   $203.30  
  Purchase #5 $212.61   10.281%   $234.4684   $234.47   $234.45   $234.50  
  Purchase #6 $87.53   6.267%   $93.0155   $93.02   $93.00   $93.00  
  Purchase #7 $215.98   4.685%   $226.0987   $226.10   $226.10   $226.10  
  7 purchase totals = $968.12       $1,051.4904   $1,051.51   $1,051.50   $1,051.50