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 $39.81   11.120%   $44.2369   $44.24   $44.25   $44.20  
  Purchase #2 $165.59   3.734%   $171.7731   $171.77   $171.75   $171.80  
  Purchase #3 $141.98   4.467%   $148.3222   $148.32   $148.30   $148.30  
  Purchase #4 $37.37   9.654%   $40.9777   $40.98   $41.00   $41.00  
  Purchase #5 $240.71   12.118%   $269.8792   $269.88   $269.90   $269.90  
  Purchase #6 $70.52   11.512%   $78.6383   $78.64   $78.65   $78.60  
  Purchase #7 $180.41   11.413%   $201.0002   $201.00   $201.00   $201.00  
  7 purchase totals = $876.39       $954.8276   $954.83   $954.85   $954.80