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 $113.47   11.579%   $126.6087   $126.61   $126.60   $126.60  
  Purchase #2 $51.53   11.385%   $57.3967   $57.40   $57.40   $57.40  
  Purchase #3 $160.82   9.550%   $176.1783   $176.18   $176.20   $176.20  
  Purchase #4 $151.44   12.499%   $170.3685   $170.37   $170.35   $170.40  
  Purchase #5 $43.44   12.519%   $48.8783   $48.88   $48.90   $48.90  
  Purchase #6 $142.74   6.494%   $152.0095   $152.01   $152.00   $152.00  
  Purchase #7 $215.79   6.620%   $230.0753   $230.08   $230.10   $230.10  
  7 purchase totals = $879.23       $961.5153   $961.53   $961.55   $961.60