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 $33.79   3.517%   $34.9784   $34.98   $35.00   $35.00  
  Purchase #2 $238.89   5.412%   $251.8187   $251.82   $251.80   $251.80  
  Purchase #3 $204.53   5.278%   $215.3251   $215.33   $215.35   $215.30  
  Purchase #4 $203.42   4.490%   $212.5536   $212.55   $212.55   $212.60  
  Purchase #5 $24.79   11.350%   $27.6037   $27.60   $27.60   $27.60  
  Purchase #6 $209.60   4.470%   $218.9691   $218.97   $218.95   $219.00  
  Purchase #7 $37.83   4.419%   $39.5017   $39.50   $39.50   $39.50  
  7 purchase totals = $952.85       $1,000.7503   $1,000.75   $1,000.75   $1,000.80