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 $64.95   13.454%   $73.6884   $73.69   $73.70   $73.70  
  Purchase #2 $177.98   8.573%   $193.2382   $193.24   $193.25   $193.20  
  Purchase #3 $48.65   6.319%   $51.7242   $51.72   $51.70   $51.70  
  Purchase #4 $110.29   10.672%   $122.0601   $122.06   $122.05   $122.10  
  Purchase #5 $121.47   7.701%   $130.8244   $130.82   $130.80   $130.80  
  Purchase #6 $165.56   13.561%   $188.0116   $188.01   $188.00   $188.00  
  Purchase #7 $213.67   12.797%   $241.0133   $241.01   $241.00   $241.00  
  7 purchase totals = $902.57       $1,000.5602   $1,000.55   $1,000.50   $1,000.50