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 $147.73   11.367%   $164.5225   $164.52   $164.50   $164.50  
  Purchase #2 $211.25   6.393%   $224.7552   $224.76   $224.75   $224.80  
  Purchase #3 $64.52   9.547%   $70.6797   $70.68   $70.70   $70.70  
  Purchase #4 $241.92   5.493%   $255.2087   $255.21   $255.20   $255.20  
  Purchase #5 $177.79   9.104%   $193.976   $193.98   $194.00   $194.00  
  Purchase #6 $231.78   13.864%   $263.914   $263.91   $263.90   $263.90  
  Purchase #7 $111.86   8.756%   $121.6545   $121.65   $121.65   $121.70  
  7 purchase totals = $1,186.85       $1,294.7106   $1,294.71   $1,294.70   $1,294.80