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 $41.51   4.397%   $43.3352   $43.34   $43.35   $43.30  
  Purchase #2 $213.42   6.255%   $226.7694   $226.77   $226.75   $226.80  
  Purchase #3 $10.46   5.235%   $11.0076   $11.01   $11.00   $11.00  
  Purchase #4 $227.30   11.334%   $253.0622   $253.06   $253.05   $253.10  
  Purchase #5 $44.89   12.742%   $50.6099   $50.61   $50.60   $50.60  
  Purchase #6 $90.39   13.457%   $102.5538   $102.55   $102.55   $102.60  
  Purchase #7 $230.60   10.445%   $254.6862   $254.69   $254.70   $254.70  
  7 purchase totals = $858.57       $942.0243   $942.03   $942.00   $942.10