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 $153.67   5.612%   $162.294   $162.29   $162.30   $162.30  
  Purchase #2 $234.59   12.742%   $264.4815   $264.48   $264.50   $264.50  
  Purchase #3 $75.95   12.551%   $85.4825   $85.48   $85.50   $85.50  
  Purchase #4 $213.53   9.770%   $234.3919   $234.39   $234.40   $234.40  
  Purchase #5 $93.52   8.716%   $101.6712   $101.67   $101.65   $101.70  
  Purchase #6 $54.33   7.190%   $58.2363   $58.24   $58.25   $58.20  
  Purchase #7 $145.56   5.667%   $153.8089   $153.81   $153.80   $153.80  
  7 purchase totals = $971.15       $1,060.3663   $1,060.36   $1,060.40   $1,060.40