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 $152.89   7.317%   $164.077   $164.08   $164.10   $164.10  
  Purchase #2 $211.68   10.265%   $233.409   $233.41   $233.40   $233.40  
  Purchase #3 $11.39   7.311%   $12.2227   $12.22   $12.20   $12.20  
  Purchase #4 $149.58   11.774%   $167.1915   $167.19   $167.20   $167.20  
  Purchase #5 $84.69   4.703%   $88.673   $88.67   $88.65   $88.70  
  Purchase #6 $244.41   10.345%   $269.6942   $269.69   $269.70   $269.70  
  Purchase #7 $65.44   4.865%   $68.6237   $68.62   $68.60   $68.60  
  7 purchase totals = $920.08       $1,003.8911   $1,003.88   $1,003.85   $1,003.90