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 $246.55   7.213%   $264.3337   $264.33   $264.35   $264.30  
  Purchase #2 $177.96   7.721%   $191.7003   $191.70   $191.70   $191.70  
  Purchase #3 $219.78   10.389%   $242.6129   $242.61   $242.60   $242.60  
  Purchase #4 $10.60   13.429%   $12.0235   $12.02   $12.00   $12.00  
  Purchase #5 $84.55   13.707%   $96.1393   $96.14   $96.15   $96.10  
  Purchase #6 $196.95   11.778%   $220.1468   $220.15   $220.15   $220.10  
  Purchase #7 $212.51   10.172%   $234.1265   $234.13   $234.15   $234.10  
  7 purchase totals = $1,148.90       $1,261.0830   $1,261.08   $1,261.10   $1,260.90