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 $113.43   5.655%   $119.8445   $119.84   $119.85   $119.80  
  Purchase #2 $121.71   11.344%   $135.5168   $135.52   $135.50   $135.50  
  Purchase #3 $12.62   11.148%   $14.0269   $14.03   $14.05   $14.00  
  Purchase #4 $175.33   4.251%   $182.7833   $182.78   $182.80   $182.80  
  Purchase #5 $189.74   13.147%   $214.6851   $214.69   $214.70   $214.70  
  Purchase #6 $110.26   4.493%   $115.214   $115.21   $115.20   $115.20  
  Purchase #7 $229.94   9.809%   $252.4948   $252.49   $252.50   $252.50  
  7 purchase totals = $953.03       $1,034.5654   $1,034.56   $1,034.60   $1,034.50