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 $61.62   6.622%   $65.7005   $65.70   $65.70   $65.70  
  Purchase #2 $219.28   10.257%   $241.7715   $241.77   $241.75   $241.80  
  Purchase #3 $212.67   13.222%   $240.7892   $240.79   $240.80   $240.80  
  Purchase #4 $61.49   4.762%   $64.4182   $64.42   $64.40   $64.40  
  Purchase #5 $220.96   6.741%   $235.8549   $235.85   $235.85   $235.90  
  Purchase #6 $202.53   4.590%   $211.8261   $211.83   $211.85   $211.80  
  Purchase #7 $166.99   12.280%   $187.4964   $187.50   $187.50   $187.50  
  7 purchase totals = $1,145.54       $1,247.8568   $1,247.86   $1,247.85   $1,247.90