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 $205.97   7.779%   $221.9924   $221.99   $222.00   $222.00  
  Purchase #2 $230.63   9.122%   $251.6681   $251.67   $251.65   $251.70  
  Purchase #3 $85.46   11.742%   $95.4947   $95.49   $95.50   $95.50  
  Purchase #4 $189.79   8.548%   $206.0132   $206.01   $206.00   $206.00  
  Purchase #5 $94.64   13.675%   $107.582   $107.58   $107.60   $107.60  
  Purchase #6 $24.78   3.701%   $25.6971   $25.70   $25.70   $25.70  
  Purchase #7 $129.99   6.561%   $138.5186   $138.52   $138.50   $138.50  
  7 purchase totals = $961.26       $1,046.9661   $1,046.96   $1,046.95   $1,047.00