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 $78.98   7.758%   $85.1073   $85.11   $85.10   $85.10  
  Purchase #2 $116.65   11.199%   $129.7136   $129.71   $129.70   $129.70  
  Purchase #3 $169.45   11.735%   $189.335   $189.34   $189.35   $189.30  
  Purchase #4 $129.79   5.270%   $136.6299   $136.63   $136.65   $136.60  
  Purchase #5 $141.91   6.323%   $150.883   $150.88   $150.90   $150.90  
  Purchase #6 $208.67   6.758%   $222.7719   $222.77   $222.75   $222.80  
  Purchase #7 $240.58   4.342%   $251.026   $251.03   $251.05   $251.00  
  7 purchase totals = $1,086.03       $1,165.4667   $1,165.47   $1,165.50   $1,165.40