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 $45.77   10.460%   $50.5575   $50.56   $50.55   $50.60  
  Purchase #2 $131.42   11.135%   $146.0536   $146.05   $146.05   $146.10  
  Purchase #3 $211.47   7.805%   $227.9752   $227.98   $228.00   $228.00  
  Purchase #4 $245.66   10.853%   $272.3215   $272.32   $272.30   $272.30  
  Purchase #5 $52.32   12.458%   $58.838   $58.84   $58.85   $58.80  
  Purchase #6 $160.26   8.338%   $173.6225   $173.62   $173.60   $173.60  
  Purchase #7 $161.83   8.112%   $174.9576   $174.96   $174.95   $175.00  
  7 purchase totals = $1,008.73       $1,104.3259   $1,104.33   $1,104.30   $1,104.40