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 $76.30   10.239%   $84.1124   $84.11   $84.10   $84.10  
  Purchase #2 $194.84   3.303%   $201.2756   $201.28   $201.30   $201.30  
  Purchase #3 $147.31   13.668%   $167.4443   $167.44   $167.45   $167.40  
  Purchase #4 $36.75   13.481%   $41.7043   $41.70   $41.70   $41.70  
  Purchase #5 $245.44   9.614%   $269.0366   $269.04   $269.05   $269.00  
  Purchase #6 $232.66   7.153%   $249.3022   $249.30   $249.30   $249.30  
  Purchase #7 $11.27   9.353%   $12.3241   $12.32   $12.30   $12.30  
  7 purchase totals = $944.57       $1,025.1995   $1,025.19   $1,025.20   $1,025.10