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 $109.57   8.467%   $118.8473   $118.85   $118.85   $118.80  
  Purchase #2 $205.33   10.234%   $226.3435   $226.34   $226.35   $226.30  
  Purchase #3 $22.67   12.855%   $25.5842   $25.58   $25.60   $25.60  
  Purchase #4 $40.40   10.697%   $44.7216   $44.72   $44.70   $44.70  
  Purchase #5 $143.39   11.309%   $159.606   $159.61   $159.60   $159.60  
  Purchase #6 $41.45   11.569%   $46.2454   $46.25   $46.25   $46.20  
  Purchase #7 $75.40   11.801%   $84.298   $84.30   $84.30   $84.30  
  7 purchase totals = $638.21       $705.6460   $705.65   $705.65   $705.50