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 $156.74   11.664%   $175.0222   $175.02   $175.00   $175.00  
  Purchase #2 $89.84   13.193%   $101.6926   $101.69   $101.70   $101.70  
  Purchase #3 $97.80   9.863%   $107.446   $107.45   $107.45   $107.40  
  Purchase #4 $61.58   4.228%   $64.1836   $64.18   $64.20   $64.20  
  Purchase #5 $250.81   4.467%   $262.0137   $262.01   $262.00   $262.00  
  Purchase #6 $219.69   3.772%   $227.9767   $227.98   $228.00   $228.00  
  Purchase #7 $104.44   8.376%   $113.1879   $113.19   $113.20   $113.20  
  7 purchase totals = $980.90       $1,051.5227   $1,051.52   $1,051.55   $1,051.50