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 $117.49   10.241%   $129.5222   $129.52   $129.50   $129.50  
  Purchase #2 $138.98   9.353%   $151.9788   $151.98   $152.00   $152.00  
  Purchase #3 $22.86   7.487%   $24.5715   $24.57   $24.55   $24.60  
  Purchase #4 $194.65   3.431%   $201.3284   $201.33   $201.35   $201.30  
  Purchase #5 $168.57   4.565%   $176.2652   $176.27   $176.25   $176.30  
  Purchase #6 $108.37   4.515%   $113.2629   $113.26   $113.25   $113.30  
  Purchase #7 $199.70   7.806%   $215.2886   $215.29   $215.30   $215.30  
  7 purchase totals = $950.62       $1,012.2176   $1,012.22   $1,012.20   $1,012.30