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 $31.59   13.476%   $35.8471   $35.85   $35.85   $35.80  
  Purchase #2 $124.74   13.572%   $141.6697   $141.67   $141.65   $141.70  
  Purchase #3 $61.62   11.464%   $68.6841   $68.68   $68.70   $68.70  
  Purchase #4 $221.58   5.115%   $232.9138   $232.91   $232.90   $232.90  
  Purchase #5 $82.79   10.858%   $91.7793   $91.78   $91.80   $91.80  
  Purchase #6 $193.35   10.145%   $212.9654   $212.97   $212.95   $213.00  
  Purchase #7 $222.52   8.698%   $241.8748   $241.87   $241.85   $241.90  
  7 purchase totals = $938.19       $1,025.7342   $1,025.73   $1,025.70   $1,025.80