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 $191.69   6.842%   $204.8054   $204.81   $204.80   $204.80  
  Purchase #2 $240.95   11.225%   $267.9966   $268.00   $268.00   $268.00  
  Purchase #3 $139.89   11.400%   $155.8375   $155.84   $155.85   $155.80  
  Purchase #4 $245.44   7.796%   $264.5745   $264.57   $264.55   $264.60  
  Purchase #5 $41.65   9.813%   $45.7371   $45.74   $45.75   $45.70  
  Purchase #6 $246.91   10.246%   $272.2084   $272.21   $272.20   $272.20  
  Purchase #7 $88.64   7.560%   $95.3412   $95.34   $95.35   $95.30  
  7 purchase totals = $1,195.17       $1,306.5007   $1,306.51   $1,306.50   $1,306.40