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 $181.86   8.317%   $196.9853   $196.99   $197.00   $197.00  
  Purchase #2 $57.68   8.740%   $62.7212   $62.72   $62.70   $62.70  
  Purchase #3 $26.57   3.739%   $27.5635   $27.56   $27.55   $27.60  
  Purchase #4 $205.62   8.598%   $223.2992   $223.30   $223.30   $223.30  
  Purchase #5 $134.34   9.707%   $147.3804   $147.38   $147.40   $147.40  
  Purchase #6 $247.38   4.107%   $257.5399   $257.54   $257.55   $257.50  
  Purchase #7 $239.56   8.244%   $259.3093   $259.31   $259.30   $259.30  
  7 purchase totals = $1,093.01       $1,174.7988   $1,174.80   $1,174.80   $1,174.80