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 $250.65   5.401%   $264.1876   $264.19   $264.20   $264.20  
  Purchase #2 $61.56   13.338%   $69.7709   $69.77   $69.75   $69.80  
  Purchase #3 $132.86   11.376%   $147.9742   $147.97   $147.95   $148.00  
  Purchase #4 $138.89   6.226%   $147.5373   $147.54   $147.55   $147.50  
  Purchase #5 $167.82   4.695%   $175.6991   $175.70   $175.70   $175.70  
  Purchase #6 $122.68   13.690%   $139.4749   $139.47   $139.45   $139.50  
  Purchase #7 $7.43   13.347%   $8.4217   $8.42   $8.40   $8.40  
  7 purchase totals = $881.89       $953.0657   $953.06   $953.00   $953.10