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 $166.97   5.395%   $175.978   $175.98   $176.00   $176.00  
  Purchase #2 $27.93   13.198%   $31.6162   $31.62   $31.60   $31.60  
  Purchase #3 $141.57   6.127%   $150.244   $150.24   $150.25   $150.20  
  Purchase #4 $219.78   6.639%   $234.3712   $234.37   $234.35   $234.40  
  Purchase #5 $11.89   6.132%   $12.6191   $12.62   $12.60   $12.60  
  Purchase #6 $239.56   8.216%   $259.2422   $259.24   $259.25   $259.20  
  Purchase #7 $121.89   12.406%   $137.0117   $137.01   $137.00   $137.00  
  7 purchase totals = $929.59       $1,001.0824   $1,001.08   $1,001.05   $1,001.00