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 $81.98   4.595%   $85.747   $85.75   $85.75   $85.70  
  Purchase #2 $145.96   8.748%   $158.7286   $158.73   $158.75   $158.70  
  Purchase #3 $220.85   5.634%   $233.2927   $233.29   $233.30   $233.30  
  Purchase #4 $81.95   7.541%   $88.1298   $88.13   $88.15   $88.10  
  Purchase #5 $229.78   9.532%   $251.6826   $251.68   $251.70   $251.70  
  Purchase #6 $52.82   9.432%   $57.802   $57.80   $57.80   $57.80  
  Purchase #7 $69.44   9.342%   $75.9271   $75.93   $75.95   $75.90  
  7 purchase totals = $882.78       $951.3098   $951.31   $951.40   $951.20