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 $227.36   11.585%   $253.6997   $253.70   $253.70   $253.70  
  Purchase #2 $169.50   9.766%   $186.0534   $186.05   $186.05   $186.10  
  Purchase #3 $238.95   3.556%   $247.4471   $247.45   $247.45   $247.40  
  Purchase #4 $228.64   6.540%   $243.5931   $243.59   $243.60   $243.60  
  Purchase #5 $189.97   11.107%   $211.07   $211.07   $211.05   $211.10  
  Purchase #6 $210.99   10.350%   $232.8275   $232.83   $232.85   $232.80  
  Purchase #7 $66.78   5.591%   $70.5137   $70.51   $70.50   $70.50  
  7 purchase totals = $1,332.19       $1,445.2045   $1,445.20   $1,445.20   $1,445.20