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 $228.82   10.615%   $253.1092   $253.11   $253.10   $253.10  
  Purchase #2 $200.89   12.753%   $226.5095   $226.51   $226.50   $226.50  
  Purchase #3 $12.70   10.144%   $13.9883   $13.99   $14.00   $14.00  
  Purchase #4 $22.61   10.128%   $24.8999   $24.90   $24.90   $24.90  
  Purchase #5 $46.89   6.292%   $49.8403   $49.84   $49.85   $49.80  
  Purchase #6 $149.62   11.654%   $167.0567   $167.06   $167.05   $167.10  
  Purchase #7 $246.79   11.472%   $275.1017   $275.10   $275.10   $275.10  
  7 purchase totals = $908.32       $1,010.5056   $1,010.51   $1,010.50   $1,010.50