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 $67.57   3.746%   $70.1012   $70.10   $70.10   $70.10  
  Purchase #2 $183.86   5.868%   $194.6489   $194.65   $194.65   $194.60  
  Purchase #3 $27.58   5.158%   $29.0026   $29.00   $29.00   $29.00  
  Purchase #4 $216.41   13.353%   $245.3072   $245.31   $245.30   $245.30  
  Purchase #5 $116.85   13.720%   $132.8818   $132.88   $132.90   $132.90  
  Purchase #6 $107.89   12.558%   $121.4388   $121.44   $121.45   $121.40  
  Purchase #7 $202.45   4.129%   $210.8092   $210.81   $210.80   $210.80  
  7 purchase totals = $922.61       $1,004.1897   $1,004.19   $1,004.20   $1,004.10