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 $238.87   11.297%   $265.8551   $265.86   $265.85   $265.90  
  Purchase #2 $165.64   13.322%   $187.7066   $187.71   $187.70   $187.70  
  Purchase #3 $86.75   11.628%   $96.8373   $96.84   $96.85   $96.80  
  Purchase #4 $33.67   7.757%   $36.2818   $36.28   $36.30   $36.30  
  Purchase #5 $39.64   8.558%   $43.0324   $43.03   $43.05   $43.00  
  Purchase #6 $126.80   5.301%   $133.5217   $133.52   $133.50   $133.50  
  Purchase #7 $235.51   7.348%   $252.8153   $252.82   $252.80   $252.80  
  7 purchase totals = $926.88       $1,016.0502   $1,016.06   $1,016.05   $1,016.00