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 $216.29   11.563%   $241.2996   $241.30   $241.30   $241.30  
  Purchase #2 $105.72   7.507%   $113.6564   $113.66   $113.65   $113.70  
  Purchase #3 $140.74   3.535%   $145.7152   $145.72   $145.70   $145.70  
  Purchase #4 $198.81   7.229%   $213.182   $213.18   $213.20   $213.20  
  Purchase #5 $160.75   9.229%   $175.5856   $175.59   $175.60   $175.60  
  Purchase #6 $149.82   8.867%   $163.1045   $163.10   $163.10   $163.10  
  Purchase #7 $100.79   6.142%   $106.9805   $106.98   $107.00   $107.00  
  7 purchase totals = $1,072.92       $1,159.5238   $1,159.53   $1,159.55   $1,159.60