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 $136.85   11.330%   $152.3551   $152.36   $152.35   $152.40  
  Purchase #2 $203.34   4.679%   $212.8543   $212.85   $212.85   $212.90  
  Purchase #3 $58.94   10.642%   $65.2124   $65.21   $65.20   $65.20  
  Purchase #4 $211.66   6.370%   $225.1427   $225.14   $225.15   $225.10  
  Purchase #5 $203.34   8.840%   $221.3153   $221.32   $221.30   $221.30  
  Purchase #6 $95.27   13.676%   $108.2991   $108.30   $108.30   $108.30  
  Purchase #7 $66.88   11.179%   $74.3565   $74.36   $74.35   $74.40  
  7 purchase totals = $976.28       $1,059.5354   $1,059.54   $1,059.50   $1,059.60