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 $79.36   10.284%   $87.5214   $87.52   $87.50   $87.50  
  Purchase #2 $46.83   8.356%   $50.7431   $50.74   $50.75   $50.70  
  Purchase #3 $113.67   5.137%   $119.5092   $119.51   $119.50   $119.50  
  Purchase #4 $106.28   10.833%   $117.7933   $117.79   $117.80   $117.80  
  Purchase #5 $23.51   4.506%   $24.5694   $24.57   $24.55   $24.60  
  Purchase #6 $190.91   10.502%   $210.9594   $210.96   $210.95   $211.00  
  Purchase #7 $116.73   12.415%   $131.222   $131.22   $131.20   $131.20  
  7 purchase totals = $677.29       $742.3178   $742.31   $742.25   $742.30