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 $69.75   11.185%   $77.5515   $77.55   $77.55   $77.60  
  Purchase #2 $207.65   6.741%   $221.6477   $221.65   $221.65   $221.60  
  Purchase #3 $101.48   4.583%   $106.1308   $106.13   $106.15   $106.10  
  Purchase #4 $152.83   6.626%   $162.9565   $162.96   $162.95   $163.00  
  Purchase #5 $247.71   12.842%   $279.5209   $279.52   $279.50   $279.50  
  Purchase #6 $52.92   11.174%   $58.8333   $58.83   $58.85   $58.80  
  Purchase #7 $189.50   11.803%   $211.8667   $211.87   $211.85   $211.90  
  7 purchase totals = $1,021.84       $1,118.5074   $1,118.51   $1,118.50   $1,118.50