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 $43.31   13.513%   $49.1625   $49.16   $49.15   $49.20  
  Purchase #2 $196.75   11.350%   $219.0811   $219.08   $219.10   $219.10  
  Purchase #3 $196.59   12.559%   $221.2797   $221.28   $221.30   $221.30  
  Purchase #4 $58.40   4.646%   $61.1133   $61.11   $61.10   $61.10  
  Purchase #5 $232.88   13.319%   $263.8973   $263.90   $263.90   $263.90  
  Purchase #6 $39.58   3.257%   $40.8691   $40.87   $40.85   $40.90  
  Purchase #7 $193.73   4.382%   $202.2192   $202.22   $202.20   $202.20  
  7 purchase totals = $961.24       $1,057.6222   $1,057.62   $1,057.60   $1,057.70