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 $41.54   12.272%   $46.6378   $46.64   $46.65   $46.60  
  Purchase #2 $189.88   7.436%   $203.9995   $204.00   $204.00   $204.00  
  Purchase #3 $116.30   9.483%   $127.3287   $127.33   $127.35   $127.30  
  Purchase #4 $184.96   10.422%   $204.2365   $204.24   $204.25   $204.20  
  Purchase #5 $214.56   9.303%   $234.5205   $234.52   $234.50   $234.50  
  Purchase #6 $132.50   12.494%   $149.0546   $149.05   $149.05   $149.10  
  Purchase #7 $237.47   6.191%   $252.1718   $252.17   $252.15   $252.20  
  7 purchase totals = $1,117.21       $1,217.9494   $1,217.95   $1,217.95   $1,217.90