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 $85.88   10.370%   $94.7858   $94.79   $94.80   $94.80  
  Purchase #2 $243.85   13.668%   $277.1794   $277.18   $277.20   $277.20  
  Purchase #3 $221.43   10.428%   $244.5207   $244.52   $244.50   $244.50  
  Purchase #4 $212.79   6.305%   $226.2064   $226.21   $226.20   $226.20  
  Purchase #5 $128.54   7.485%   $138.1612   $138.16   $138.15   $138.20  
  Purchase #6 $141.60   8.836%   $154.1118   $154.11   $154.10   $154.10  
  Purchase #7 $170.29   12.349%   $191.3191   $191.32   $191.30   $191.30  
  7 purchase totals = $1,204.38       $1,326.2844   $1,326.29   $1,326.25   $1,326.30