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 $67.99   8.571%   $73.8174   $73.82   $73.80   $73.80  
  Purchase #2 $184.93   9.243%   $202.0231   $202.02   $202.00   $202.00  
  Purchase #3 $133.29   9.766%   $146.3071   $146.31   $146.30   $146.30  
  Purchase #4 $203.90   11.290%   $226.9203   $226.92   $226.90   $226.90  
  Purchase #5 $94.44   8.836%   $102.7847   $102.78   $102.80   $102.80  
  Purchase #6 $189.61   7.108%   $203.0875   $203.09   $203.10   $203.10  
  Purchase #7 $95.96   7.647%   $103.2981   $103.30   $103.30   $103.30  
  7 purchase totals = $970.12       $1,058.2382   $1,058.24   $1,058.20   $1,058.20