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 $83.42   9.320%   $91.1947   $91.19   $91.20   $91.20  
  Purchase #2 $118.98   13.450%   $134.9828   $134.98   $135.00   $135.00  
  Purchase #3 $157.91   7.548%   $169.829   $169.83   $169.85   $169.80  
  Purchase #4 $168.25   8.146%   $181.9556   $181.96   $181.95   $182.00  
  Purchase #5 $74.67   11.194%   $83.0286   $83.03   $83.05   $83.00  
  Purchase #6 $200.58   10.643%   $221.9277   $221.93   $221.95   $221.90  
  Purchase #7 $164.79   4.862%   $172.8021   $172.80   $172.80   $172.80  
  7 purchase totals = $968.60       $1,055.7205   $1,055.72   $1,055.80   $1,055.70