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 $84.47   3.740%   $87.6292   $87.63   $87.65   $87.60  
  Purchase #2 $188.64   8.421%   $204.5254   $204.53   $204.55   $204.50  
  Purchase #3 $167.36   5.173%   $176.0175   $176.02   $176.00   $176.00  
  Purchase #4 $83.50   8.510%   $90.6059   $90.61   $90.60   $90.60  
  Purchase #5 $104.47   9.163%   $114.0426   $114.04   $114.05   $114.00  
  Purchase #6 $166.35   3.657%   $172.4334   $172.43   $172.45   $172.40  
  Purchase #7 $241.93   7.790%   $260.7763   $260.78   $260.80   $260.80  
  7 purchase totals = $1,036.72       $1,106.0303   $1,106.04   $1,106.10   $1,105.90