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 $84.83   4.697%   $88.8145   $88.81   $88.80   $88.80  
  Purchase #2 $116.27   12.212%   $130.4689   $130.47   $130.45   $130.50  
  Purchase #3 $191.51   5.366%   $201.7864   $201.79   $201.80   $201.80  
  Purchase #4 $226.82   5.571%   $239.4561   $239.46   $239.45   $239.50  
  Purchase #5 $12.37   13.325%   $14.0183   $14.02   $14.00   $14.00  
  Purchase #6 $149.33   8.563%   $162.1171   $162.12   $162.10   $162.10  
  Purchase #7 $211.29   5.836%   $223.6209   $223.62   $223.60   $223.60  
  7 purchase totals = $992.42       $1,060.2822   $1,060.29   $1,060.20   $1,060.30