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 $87.95   7.576%   $94.6131   $94.61   $94.60   $94.60  
  Purchase #2 $128.92   8.424%   $139.7802   $139.78   $139.80   $139.80  
  Purchase #3 $166.61   12.286%   $187.0797   $187.08   $187.10   $187.10  
  Purchase #4 $31.53   9.793%   $34.6177   $34.62   $34.60   $34.60  
  Purchase #5 $79.94   5.369%   $84.232   $84.23   $84.25   $84.20  
  Purchase #6 $236.65   13.759%   $269.2107   $269.21   $269.20   $269.20  
  Purchase #7 $246.99   13.409%   $280.1089   $280.11   $280.10   $280.10  
  7 purchase totals = $978.59       $1,089.6423   $1,089.64   $1,089.65   $1,089.60