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 $32.61   7.244%   $34.9723   $34.97   $34.95   $35.00  
  Purchase #2 $212.69   11.342%   $236.8133   $236.81   $236.80   $236.80  
  Purchase #3 $158.83   7.873%   $171.3347   $171.33   $171.35   $171.30  
  Purchase #4 $183.39   6.147%   $194.663   $194.66   $194.65   $194.70  
  Purchase #5 $135.72   5.498%   $143.1819   $143.18   $143.20   $143.20  
  Purchase #6 $71.39   5.530%   $75.3379   $75.34   $75.35   $75.30  
  Purchase #7 $22.66   10.482%   $25.0352   $25.04   $25.05   $25.00  
  7 purchase totals = $817.29       $881.3383   $881.33   $881.35   $881.30