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 $13.40   8.764%   $14.5744   $14.57   $14.55   $14.60  
  Purchase #2 $241.52   4.775%   $253.0526   $253.05   $253.05   $253.10  
  Purchase #3 $215.39   13.521%   $244.5129   $244.51   $244.50   $244.50  
  Purchase #4 $5.55   11.597%   $6.1936   $6.19   $6.20   $6.20  
  Purchase #5 $49.53   12.188%   $55.5667   $55.57   $55.55   $55.60  
  Purchase #6 $193.62   8.761%   $210.583   $210.58   $210.60   $210.60  
  Purchase #7 $212.65   9.676%   $233.226   $233.23   $233.25   $233.20  
  7 purchase totals = $931.66       $1,017.7092   $1,017.70   $1,017.70   $1,017.80