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 $56.98   4.793%   $59.7111   $59.71   $59.70   $59.70  
  Purchase #2 $133.85   9.581%   $146.6742   $146.67   $146.65   $146.70  
  Purchase #3 $107.31   12.842%   $121.0908   $121.09   $121.10   $121.10  
  Purchase #4 $188.75   9.114%   $205.9527   $205.95   $205.95   $206.00  
  Purchase #5 $180.43   9.293%   $197.1974   $197.20   $197.20   $197.20  
  Purchase #6 $179.96   12.767%   $202.9355   $202.94   $202.95   $202.90  
  Purchase #7 $104.83   10.835%   $116.1883   $116.19   $116.20   $116.20  
  7 purchase totals = $952.11       $1,049.7500   $1,049.75   $1,049.75   $1,049.80