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 $186.44   8.455%   $202.2035   $202.20   $202.20   $202.20  
  Purchase #2 $23.54   10.159%   $25.9314   $25.93   $25.95   $25.90  
  Purchase #3 $228.89   11.861%   $256.0386   $256.04   $256.05   $256.00  
  Purchase #4 $24.95   9.497%   $27.3195   $27.32   $27.30   $27.30  
  Purchase #5 $150.56   11.391%   $167.7103   $167.71   $167.70   $167.70  
  Purchase #6 $186.40   8.178%   $201.6438   $201.64   $201.65   $201.60  
  Purchase #7 $173.41   9.224%   $189.4053   $189.41   $189.40   $189.40  
  7 purchase totals = $974.19       $1,070.2524   $1,070.25   $1,070.25   $1,070.10