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 $153.31   10.712%   $169.7326   $169.73   $169.75   $169.70  
  Purchase #2 $236.52   9.796%   $259.6895   $259.69   $259.70   $259.70  
  Purchase #3 $24.35   13.544%   $27.648   $27.65   $27.65   $27.60  
  Purchase #4 $159.75   5.286%   $168.1944   $168.19   $168.20   $168.20  
  Purchase #5 $101.99   6.855%   $108.9814   $108.98   $109.00   $109.00  
  Purchase #6 $119.43   12.776%   $134.6884   $134.69   $134.70   $134.70  
  Purchase #7 $143.82   10.332%   $158.6795   $158.68   $158.70   $158.70  
  7 purchase totals = $939.17       $1,027.6138   $1,027.61   $1,027.70   $1,027.60