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 $32.84   3.842%   $34.1017   $34.10   $34.10   $34.10  
  Purchase #2 $236.28   11.594%   $263.6743   $263.67   $263.65   $263.70  
  Purchase #3 $102.80   13.296%   $116.4683   $116.47   $116.45   $116.50  
  Purchase #4 $183.41   6.363%   $195.0804   $195.08   $195.10   $195.10  
  Purchase #5 $229.29   7.852%   $247.2939   $247.29   $247.30   $247.30  
  Purchase #6 $204.67   8.309%   $221.676   $221.68   $221.70   $221.70  
  Purchase #7 $204.95   3.860%   $212.8611   $212.86   $212.85   $212.90  
  7 purchase totals = $1,194.24       $1,291.1557   $1,291.15   $1,291.15   $1,291.30