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 $132.72   9.273%   $145.0271   $145.03   $145.05   $145.00  
  Purchase #2 $91.84   4.608%   $96.072   $96.07   $96.05   $96.10  
  Purchase #3 $51.74   12.321%   $58.1149   $58.11   $58.10   $58.10  
  Purchase #4 $138.52   7.772%   $149.2858   $149.29   $149.30   $149.30  
  Purchase #5 $40.62   3.640%   $42.0986   $42.10   $42.10   $42.10  
  Purchase #6 $62.27   13.538%   $70.7001   $70.70   $70.70   $70.70  
  Purchase #7 $32.63   9.277%   $35.6571   $35.66   $35.65   $35.70  
  7 purchase totals = $550.34       $596.9556   $596.96   $596.95   $597.00