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 $146.59   10.245%   $161.6081   $161.61   $161.60   $161.60  
  Purchase #2 $136.37   6.761%   $145.59   $145.59   $145.60   $145.60  
  Purchase #3 $29.68   11.485%   $33.0887   $33.09   $33.10   $33.10  
  Purchase #4 $226.25   12.613%   $254.7869   $254.79   $254.80   $254.80  
  Purchase #5 $221.77   12.384%   $249.234   $249.23   $249.25   $249.20  
  Purchase #6 $201.27   5.814%   $212.9718   $212.97   $212.95   $213.00  
  Purchase #7 $115.36   11.118%   $128.1857   $128.19   $128.20   $128.20  
  7 purchase totals = $1,077.29       $1,185.4652   $1,185.47   $1,185.50   $1,185.50