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 $185.26   13.363%   $210.0163   $210.02   $210.00   $210.00  
  Purchase #2 $31.25   12.327%   $35.1022   $35.10   $35.10   $35.10  
  Purchase #3 $106.91   11.538%   $119.2453   $119.25   $119.25   $119.20  
  Purchase #4 $174.84   7.495%   $187.9443   $187.94   $187.95   $187.90  
  Purchase #5 $78.43   7.529%   $84.335   $84.34   $84.35   $84.30  
  Purchase #6 $236.59   6.350%   $251.6135   $251.61   $251.60   $251.60  
  Purchase #7 $114.55   3.542%   $118.6074   $118.61   $118.60   $118.60  
  7 purchase totals = $927.83       $1,006.8640   $1,006.87   $1,006.85   $1,006.70