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 $147.59   13.799%   $167.9559   $167.96   $167.95   $168.00  
  Purchase #2 $158.31   9.690%   $173.6502   $173.65   $173.65   $173.70  
  Purchase #3 $8.38   13.148%   $9.4818   $9.48   $9.50   $9.50  
  Purchase #4 $49.68   11.504%   $55.3952   $55.40   $55.40   $55.40  
  Purchase #5 $109.78   3.384%   $113.495   $113.50   $113.50   $113.50  
  Purchase #6 $138.99   11.362%   $154.782   $154.78   $154.80   $154.80  
  Purchase #7 $165.49   7.699%   $178.2311   $178.23   $178.25   $178.20  
  7 purchase totals = $778.22       $852.9912   $853.00   $853.05   $853.10