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 $85.66   9.778%   $94.0358   $94.04   $94.05   $94.00  
  Purchase #2 $166.67   10.727%   $184.5487   $184.55   $184.55   $184.50  
  Purchase #3 $117.46   9.618%   $128.7573   $128.76   $128.75   $128.80  
  Purchase #4 $92.54   7.408%   $99.3954   $99.40   $99.40   $99.40  
  Purchase #5 $145.74   10.210%   $160.6201   $160.62   $160.60   $160.60  
  Purchase #6 $192.59   4.561%   $201.374   $201.37   $201.35   $201.40  
  Purchase #7 $140.51   9.351%   $153.6491   $153.65   $153.65   $153.60  
  7 purchase totals = $941.17       $1,022.3804   $1,022.39   $1,022.35   $1,022.30