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 $241.45   12.563%   $271.7834   $271.78   $271.80   $271.80  
  Purchase #2 $223.35   10.440%   $246.6677   $246.67   $246.65   $246.70  
  Purchase #3 $108.45   9.408%   $118.653   $118.65   $118.65   $118.70  
  Purchase #4 $170.62   5.428%   $179.8813   $179.88   $179.90   $179.90  
  Purchase #5 $150.66   5.792%   $159.3862   $159.39   $159.40   $159.40  
  Purchase #6 $32.58   9.306%   $35.6119   $35.61   $35.60   $35.60  
  Purchase #7 $58.34   6.464%   $62.1111   $62.11   $62.10   $62.10  
  7 purchase totals = $985.45       $1,074.0946   $1,074.09   $1,074.10   $1,074.20