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 $161.84   12.459%   $182.0036   $182.00   $182.00   $182.00  
  Purchase #2 $236.52   6.401%   $251.6596   $251.66   $251.65   $251.70  
  Purchase #3 $222.31   4.414%   $232.1228   $232.12   $232.10   $232.10  
  Purchase #4 $96.91   10.689%   $107.2687   $107.27   $107.25   $107.30  
  Purchase #5 $243.92   9.761%   $267.729   $267.73   $267.75   $267.70  
  Purchase #6 $246.74   8.343%   $267.3255   $267.33   $267.35   $267.30  
  Purchase #7 $63.40   4.189%   $66.0558   $66.06   $66.05   $66.10  
  7 purchase totals = $1,271.64       $1,374.1650   $1,374.17   $1,374.15   $1,374.20