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 $198.31   13.563%   $225.2068   $225.21   $225.20   $225.20  
  Purchase #2 $13.48   4.680%   $14.1109   $14.11   $14.10   $14.10  
  Purchase #3 $113.34   13.612%   $128.7678   $128.77   $128.75   $128.80  
  Purchase #4 $203.73   7.811%   $219.6434   $219.64   $219.65   $219.60  
  Purchase #5 $191.77   10.847%   $212.5713   $212.57   $212.55   $212.60  
  Purchase #6 $166.45   9.283%   $181.9016   $181.90   $181.90   $181.90  
  Purchase #7 $186.77   7.413%   $200.6153   $200.62   $200.60   $200.60  
  7 purchase totals = $1,073.85       $1,182.8171   $1,182.82   $1,182.75   $1,182.80