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 $77.50   13.576%   $88.0214   $88.02   $88.00   $88.00  
  Purchase #2 $101.59   9.843%   $111.5895   $111.59   $111.60   $111.60  
  Purchase #3 $96.39   8.150%   $104.2458   $104.25   $104.25   $104.20  
  Purchase #4 $236.80   11.847%   $264.8537   $264.85   $264.85   $264.90  
  Purchase #5 $69.97   8.545%   $75.9489   $75.95   $75.95   $75.90  
  Purchase #6 $135.30   8.653%   $147.0075   $147.01   $147.00   $147.00  
  Purchase #7 $182.99   10.851%   $202.8462   $202.85   $202.85   $202.80  
  7 purchase totals = $900.54       $994.5130   $994.52   $994.50   $994.40