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 $27.28   8.427%   $29.5789   $29.58   $29.60   $29.60  
  Purchase #2 $47.53   10.157%   $52.3576   $52.36   $52.35   $52.40  
  Purchase #3 $200.65   4.566%   $209.8117   $209.81   $209.80   $209.80  
  Purchase #4 $195.68   3.721%   $202.9613   $202.96   $202.95   $203.00  
  Purchase #5 $153.47   8.823%   $167.0107   $167.01   $167.00   $167.00  
  Purchase #6 $175.53   10.375%   $193.7412   $193.74   $193.75   $193.70  
  Purchase #7 $216.82   6.421%   $230.742   $230.74   $230.75   $230.70  
  7 purchase totals = $1,016.96       $1,086.2034   $1,086.20   $1,086.20   $1,086.20