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 $180.97   6.644%   $192.9936   $192.99   $193.00   $193.00  
  Purchase #2 $199.53   6.409%   $212.3179   $212.32   $212.30   $212.30  
  Purchase #3 $27.46   8.459%   $29.7828   $29.78   $29.80   $29.80  
  Purchase #4 $169.82   3.550%   $175.8486   $175.85   $175.85   $175.80  
  Purchase #5 $111.48   13.731%   $126.7873   $126.79   $126.80   $126.80  
  Purchase #6 $73.41   3.453%   $75.9448   $75.94   $75.95   $75.90  
  Purchase #7 $217.86   6.750%   $232.5656   $232.57   $232.55   $232.60  
  7 purchase totals = $980.53       $1,046.2406   $1,046.24   $1,046.25   $1,046.20