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 $87.32   12.657%   $98.3721   $98.37   $98.35   $98.40  
  Purchase #2 $90.44   6.873%   $96.6559   $96.66   $96.65   $96.70  
  Purchase #3 $248.28   8.487%   $269.3515   $269.35   $269.35   $269.40  
  Purchase #4 $21.37   5.113%   $22.4626   $22.46   $22.45   $22.50  
  Purchase #5 $145.96   6.653%   $155.6707   $155.67   $155.65   $155.70  
  Purchase #6 $84.66   12.717%   $95.4262   $95.43   $95.45   $95.40  
  Purchase #7 $159.44   3.661%   $165.2771   $165.28   $165.30   $165.30  
  7 purchase totals = $837.47       $903.2161   $903.22   $903.20   $903.40