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 $83.94   9.424%   $91.8505   $91.85   $91.85   $91.90  
  Purchase #2 $177.26   13.505%   $201.199   $201.20   $201.20   $201.20  
  Purchase #3 $142.51   4.172%   $148.4555   $148.46   $148.45   $148.50  
  Purchase #4 $54.99   12.282%   $61.7439   $61.74   $61.75   $61.70  
  Purchase #5 $153.55   3.726%   $159.2713   $159.27   $159.25   $159.30  
  Purchase #6 $245.94   12.524%   $276.7415   $276.74   $276.75   $276.70  
  Purchase #7 $118.51   4.322%   $123.632   $123.63   $123.65   $123.60  
  7 purchase totals = $976.70       $1,062.8937   $1,062.89   $1,062.90   $1,062.90