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 $177.42   4.252%   $184.9639   $184.96   $184.95   $185.00  
  Purchase #2 $219.56   12.291%   $246.5461   $246.55   $246.55   $246.50  
  Purchase #3 $179.84   10.765%   $199.1998   $199.20   $199.20   $199.20  
  Purchase #4 $191.70   10.409%   $211.6541   $211.65   $211.65   $211.70  
  Purchase #5 $90.75   4.629%   $94.9508   $94.95   $94.95   $95.00  
  Purchase #6 $248.40   6.414%   $264.3324   $264.33   $264.35   $264.30  
  Purchase #7 $39.92   11.268%   $44.4182   $44.42   $44.40   $44.40  
  7 purchase totals = $1,147.59       $1,246.0653   $1,246.06   $1,246.05   $1,246.10