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 $66.53   12.822%   $75.0605   $75.06   $75.05   $75.10  
  Purchase #2 $88.94   7.196%   $95.3401   $95.34   $95.35   $95.30  
  Purchase #3 $84.34   5.185%   $88.713   $88.71   $88.70   $88.70  
  Purchase #4 $137.89   7.625%   $148.4041   $148.40   $148.40   $148.40  
  Purchase #5 $195.39   10.272%   $215.4605   $215.46   $215.45   $215.50  
  Purchase #6 $249.93   13.454%   $283.5556   $283.56   $283.55   $283.60  
  Purchase #7 $62.64   11.852%   $70.0641   $70.06   $70.05   $70.10  
  7 purchase totals = $885.66       $976.5979   $976.59   $976.55   $976.70