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 $88.90   7.239%   $95.3355   $95.34   $95.35   $95.30  
  Purchase #2 $173.32   11.234%   $192.7908   $192.79   $192.80   $192.80  
  Purchase #3 $187.89   13.187%   $212.6671   $212.67   $212.65   $212.70  
  Purchase #4 $134.66   10.352%   $148.6   $148.60   $148.60   $148.60  
  Purchase #5 $104.84   4.600%   $109.6626   $109.66   $109.65   $109.70  
  Purchase #6 $176.52   4.557%   $184.564   $184.56   $184.55   $184.60  
  Purchase #7 $213.82   12.175%   $239.8526   $239.85   $239.85   $239.90  
  7 purchase totals = $1,079.95       $1,183.4726   $1,183.47   $1,183.45   $1,183.60