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 $46.64   9.790%   $51.2061   $51.21   $51.20   $51.20  
  Purchase #2 $101.37   8.524%   $110.0108   $110.01   $110.00   $110.00  
  Purchase #3 $172.89   11.591%   $192.9297   $192.93   $192.95   $192.90  
  Purchase #4 $233.47   3.811%   $242.3675   $242.37   $242.35   $242.40  
  Purchase #5 $53.39   3.753%   $55.3937   $55.39   $55.40   $55.40  
  Purchase #6 $219.61   5.791%   $232.3276   $232.33   $232.35   $232.30  
  Purchase #7 $194.56   3.591%   $201.5466   $201.55   $201.55   $201.50  
  7 purchase totals = $1,021.93       $1,085.7820   $1,085.79   $1,085.80   $1,085.70