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 $79.74   5.736%   $84.3139   $84.31   $84.30   $84.30  
  Purchase #2 $30.99   13.372%   $35.134   $35.13   $35.15   $35.10  
  Purchase #3 $227.52   10.511%   $251.4346   $251.43   $251.45   $251.40  
  Purchase #4 $130.68   6.112%   $138.6672   $138.67   $138.65   $138.70  
  Purchase #5 $183.82   5.588%   $194.0919   $194.09   $194.10   $194.10  
  Purchase #6 $221.90   12.827%   $250.3631   $250.36   $250.35   $250.40  
  Purchase #7 $96.87   10.158%   $106.7101   $106.71   $106.70   $106.70  
  7 purchase totals = $971.52       $1,060.7148   $1,060.70   $1,060.70   $1,060.70