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 $95.86   6.765%   $102.3449   $102.34   $102.35   $102.30  
  Purchase #2 $130.95   9.465%   $143.3444   $143.34   $143.35   $143.30  
  Purchase #3 $231.84   8.162%   $250.7628   $250.76   $250.75   $250.80  
  Purchase #4 $221.52   5.232%   $233.1099   $233.11   $233.10   $233.10  
  Purchase #5 $63.28   4.448%   $66.0947   $66.09   $66.10   $66.10  
  Purchase #6 $202.80   8.472%   $219.9812   $219.98   $220.00   $220.00  
  Purchase #7 $240.85   4.573%   $251.8641   $251.86   $251.85   $251.90  
  7 purchase totals = $1,187.10       $1,267.5020   $1,267.48   $1,267.50   $1,267.50