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 $31.70   13.586%   $36.0068   $36.01   $36.00   $36.00  
  Purchase #2 $194.97   12.759%   $219.8462   $219.85   $219.85   $219.80  
  Purchase #3 $70.29   6.195%   $74.6445   $74.64   $74.65   $74.60  
  Purchase #4 $111.35   11.428%   $124.0751   $124.08   $124.10   $124.10  
  Purchase #5 $12.73   4.139%   $13.2569   $13.26   $13.25   $13.30  
  Purchase #6 $109.57   9.765%   $120.2695   $120.27   $120.25   $120.30  
  Purchase #7 $164.55   5.317%   $173.2991   $173.30   $173.30   $173.30  
  7 purchase totals = $695.16       $761.3981   $761.41   $761.40   $761.40