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 $63.79   11.320%   $71.011   $71.01   $71.00   $71.00  
  Purchase #2 $181.55   7.816%   $195.7399   $195.74   $195.75   $195.70  
  Purchase #3 $58.56   4.116%   $60.9703   $60.97   $60.95   $61.00  
  Purchase #4 $17.64   13.831%   $20.0798   $20.08   $20.10   $20.10  
  Purchase #5 $138.95   6.749%   $148.3277   $148.33   $148.35   $148.30  
  Purchase #6 $113.28   4.578%   $118.466   $118.47   $118.45   $118.50  
  Purchase #7 $16.34   13.287%   $18.5111   $18.51   $18.50   $18.50  
  7 purchase totals = $590.11       $633.1058   $633.11   $633.10   $633.10