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 $66.95   12.622%   $75.4004   $75.40   $75.40   $75.40  
  Purchase #2 $132.58   9.563%   $145.2586   $145.26   $145.25   $145.30  
  Purchase #3 $152.62   11.215%   $169.7363   $169.74   $169.75   $169.70  
  Purchase #4 $107.44   8.852%   $116.9506   $116.95   $116.95   $117.00  
  Purchase #5 $100.89   7.766%   $108.7251   $108.73   $108.75   $108.70  
  Purchase #6 $219.57   11.608%   $245.0577   $245.06   $245.05   $245.10  
  Purchase #7 $140.57   6.834%   $150.1766   $150.18   $150.20   $150.20  
  7 purchase totals = $920.62       $1,011.3053   $1,011.32   $1,011.35   $1,011.40