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 $192.69   9.766%   $211.5081   $211.51   $211.50   $211.50  
  Purchase #2 $187.96   10.112%   $206.9665   $206.97   $206.95   $207.00  
  Purchase #3 $159.88   3.728%   $165.8403   $165.84   $165.85   $165.80  
  Purchase #4 $179.97   12.273%   $202.0577   $202.06   $202.05   $202.10  
  Purchase #5 $85.94   3.220%   $88.7073   $88.71   $88.70   $88.70  
  Purchase #6 $160.80   3.317%   $166.1337   $166.13   $166.15   $166.10  
  Purchase #7 $151.77   3.233%   $156.6767   $156.68   $156.70   $156.70  
  7 purchase totals = $1,119.01       $1,197.8903   $1,197.90   $1,197.90   $1,197.90