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 $46.60   13.294%   $52.795   $52.80   $52.80   $52.80  
  Purchase #2 $160.46   3.191%   $165.5803   $165.58   $165.60   $165.60  
  Purchase #3 $195.82   11.149%   $217.652   $217.65   $217.65   $217.70  
  Purchase #4 $244.72   5.741%   $258.7694   $258.77   $258.75   $258.80  
  Purchase #5 $185.45   3.177%   $191.3417   $191.34   $191.35   $191.30  
  Purchase #6 $223.46   4.415%   $233.3258   $233.33   $233.35   $233.30  
  Purchase #7 $213.75   4.104%   $222.5223   $222.52   $222.50   $222.50  
  7 purchase totals = $1,270.26       $1,341.9865   $1,341.99   $1,342.00   $1,342.00