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 $222.52   10.361%   $245.5753   $245.58   $245.60   $245.60  
  Purchase #2 $111.98   12.128%   $125.5609   $125.56   $125.55   $125.60  
  Purchase #3 $23.90   11.704%   $26.6973   $26.70   $26.70   $26.70  
  Purchase #4 $110.45   9.774%   $121.2454   $121.25   $121.25   $121.20  
  Purchase #5 $125.27   8.105%   $135.4231   $135.42   $135.40   $135.40  
  Purchase #6 $216.27   6.539%   $230.4119   $230.41   $230.40   $230.40  
  Purchase #7 $142.64   4.712%   $149.3612   $149.36   $149.35   $149.40  
  7 purchase totals = $953.03       $1,034.2751   $1,034.28   $1,034.25   $1,034.30