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 $29.51   11.219%   $32.8207   $32.82   $32.80   $32.80  
  Purchase #2 $232.87   5.380%   $245.3984   $245.40   $245.40   $245.40  
  Purchase #3 $161.40   11.793%   $180.4339   $180.43   $180.45   $180.40  
  Purchase #4 $212.99   8.820%   $231.7757   $231.78   $231.80   $231.80  
  Purchase #5 $45.58   5.551%   $48.1101   $48.11   $48.10   $48.10  
  Purchase #6 $241.98   6.433%   $257.5466   $257.55   $257.55   $257.50  
  Purchase #7 $197.62   4.273%   $206.0643   $206.06   $206.05   $206.10  
  7 purchase totals = $1,121.95       $1,202.1497   $1,202.15   $1,202.15   $1,202.10