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 $83.45   11.682%   $93.1986   $93.20   $93.20   $93.20  
  Purchase #2 $144.66   7.448%   $155.4343   $155.43   $155.45   $155.40  
  Purchase #3 $69.27   6.858%   $74.0205   $74.02   $74.00   $74.00  
  Purchase #4 $232.47   7.764%   $250.519   $250.52   $250.50   $250.50  
  Purchase #5 $106.98   12.647%   $120.5098   $120.51   $120.50   $120.50  
  Purchase #6 $192.77   12.256%   $216.3959   $216.40   $216.40   $216.40  
  Purchase #7 $110.64   5.787%   $117.0427   $117.04   $117.05   $117.00  
  7 purchase totals = $940.24       $1,027.1208   $1,027.12   $1,027.10   $1,027.00