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 $212.98   10.689%   $235.7454   $235.75   $235.75   $235.70  
  Purchase #2 $30.39   7.390%   $32.6358   $32.64   $32.65   $32.60  
  Purchase #3 $79.25   12.350%   $89.0374   $89.04   $89.05   $89.00  
  Purchase #4 $23.65   10.283%   $26.0819   $26.08   $26.10   $26.10  
  Purchase #5 $214.42   13.580%   $243.5382   $243.54   $243.55   $243.50  
  Purchase #6 $209.80   11.751%   $234.4536   $234.45   $234.45   $234.50  
  Purchase #7 $201.32   12.562%   $226.6098   $226.61   $226.60   $226.60  
  7 purchase totals = $971.81       $1,088.1021   $1,088.11   $1,088.15   $1,088.00