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 $63.46   6.134%   $67.3526   $67.35   $67.35   $67.40  
  Purchase #2 $132.95   11.276%   $147.9414   $147.94   $147.95   $147.90  
  Purchase #3 $58.48   8.436%   $63.4134   $63.41   $63.40   $63.40  
  Purchase #4 $239.27   12.577%   $269.363   $269.36   $269.35   $269.40  
  Purchase #5 $199.28   13.337%   $225.858   $225.86   $225.85   $225.90  
  Purchase #6 $94.41   6.566%   $100.609   $100.61   $100.60   $100.60  
  Purchase #7 $83.43   9.297%   $91.1865   $91.19   $91.20   $91.20  
  7 purchase totals = $871.28       $965.7239   $965.72   $965.70   $965.80