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 $210.52   8.715%   $228.8668   $228.87   $228.85   $228.90  
  Purchase #2 $121.71   12.354%   $136.7461   $136.75   $136.75   $136.70  
  Purchase #3 $11.50   5.831%   $12.1706   $12.17   $12.15   $12.20  
  Purchase #4 $204.46   12.390%   $229.7926   $229.79   $229.80   $229.80  
  Purchase #5 $171.78   12.325%   $192.9519   $192.95   $192.95   $193.00  
  Purchase #6 $186.88   8.484%   $202.7349   $202.73   $202.75   $202.70  
  Purchase #7 $84.59   11.161%   $94.0311   $94.03   $94.05   $94.00  
  7 purchase totals = $991.44       $1,097.2940   $1,097.29   $1,097.30   $1,097.30