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 $66.69   13.473%   $75.6751   $75.68   $75.70   $75.70  
  Purchase #2 $170.75   3.266%   $176.3267   $176.33   $176.35   $176.30  
  Purchase #3 $37.44   11.390%   $41.7044   $41.70   $41.70   $41.70  
  Purchase #4 $236.54   10.269%   $260.8303   $260.83   $260.85   $260.80  
  Purchase #5 $119.51   6.268%   $127.0009   $127.00   $127.00   $127.00  
  Purchase #6 $250.31   5.724%   $264.6377   $264.64   $264.65   $264.60  
  Purchase #7 $235.43   12.415%   $264.6586   $264.66   $264.65   $264.70  
  7 purchase totals = $1,116.67       $1,210.8337   $1,210.84   $1,210.90   $1,210.80